After extensive search and quite a few printed holders i wasn't quite happy with any of them, because i have different size reels and i had to move wheels each time i changed the reel. So i created my own one. It's universal, so you can put on it any size of filament up to 11cm. I also added small compartment for filament clip (if you don't need it you can print two left holders). The reason for "bumped" right part or the roller is that in smooth one reel keeps dancing left and right during printing, so you never know when it will fall off. This way reel stays put...
Since my last holder was from MartinMajewski (https://www.thingiverse.com/thing:1832235) i kept nuts and spacers from it (thanks, Martin, i hope you don't mind!)
In fact, my first version had two of these rollers on holders from Martin, so this is a solution for all Prusa owners without enclosure: just print two holders from Martin and my two rollers.
You will need to print two rollers, 4 spacers and 4 nuts. 4 nuts is best printed with resolution 0.10, other things are quite good in 0.20 resolution. Of course you can use classic metal nuts insead of printed ones, in that case it's better to user safety nuts (nylon locking) to prevent them from unwinding. Supports are only needed for left and right holder.
For assembly you need 4 pcs. of type 608 bearings and two M8 threaded rods, around 17 cm long each.
I have my printer in a box, so this holder is screwed on the top while filament is feeding through a hole down into extruder, so i added a guide, too. You must drill 20mm hole through the board and push both parts of "guide" together.
0.10 resolution is only needed for nuts (because of threads), you can use 0.20 for other things.
Use supports for left and right holders.